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I assume you have an infinite ground plane (so you specified high conductivity in the basic parameters for layer 0).
Start at the layer where you have drawn the patch. Place the two vertices where the vertical metal part should connect to the patch (this must be an edge for now). Now go the right (where you can see your layers) and select layer zero (that is the infinite groundplane).
Place a vertice directly under the last vertice that you placed on the patch's layer. So now you placed three vertices in total. right click with the mouse, this will show a menu. select "form rectangle". IE3D now automatically places a fourth vertice at the ground plane to form a vertical rectangular metal plate between ground and the edge of the patch.
If you want your connection anywhere on the patch (instead of on an edge), you first need to split the patch in at least two patches that are connected side by side. You can only connect polygons on edges of other polygons otherwise they will not be connected electrically. After splitting a larger patch in two parts, you can connect other metallic structures at the line where the two new patches connect to each other. You may need this to connect your feed to the PIFA.
There are two ways of creating a finite ground plane.
1. Set lowest layer conductivity = 0. This eliminates the ground plane (you will not see a dashed line between the small color graph for the number 0 layer).
Now you draw any ground plane you want. It is like creating land in an infinite sea. Advantage is that the radiation pattern will be close to the actual pattern of the construction. But (as far as I know), you can't use some of the feed schemes anymore. Other thing is that conductors close to ground result in steep current density change versus distance. This requires a fine meshing for the ground plane (with increased simulation time). IE3D enables finer meshing for polygons where you expect large change in current density (for example just below transmission lines close to ground).
2. Keep the infinite ground plane, but insulate the ground plane you want by drawing polygons. Note that drawing polygons on na infinite conducting layer actually removes metal. It is like digging a canal around a piece of land to create an island. The advantage is that now the metal you removed need to be meshed and this mostly saves simulation time. Disadvantage is that the radiation pattern under low elevation may differ significantly from the actual pattern. This is because in the actual circuit, you don't have the insulated infinite groundplane around it.
So if you need good pattern simulation, you need to draw the ground plane, starting from zero ground conductance and you need to use finite dielectric layers. You need to take care of the meshing.
If you are interested in circuit properties (S parameters), you can use the second method, as this reduces simulation time.
If you use option 1, I recommend you to play with it and look to the current density in the ground plane versus mesh size.
i have designed a planner inverted g antenna by making a cylindrical short ,,nd i have got vswr -1.6 at 3 ghz and return loss up to -18db but my bandwith is only 61 mhz ,,so how can i increased the bandwidth.